What do !== and === mean in PHP? [duplicate]

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Possibl开发者_运维问答e Duplicates:

How do the equality (== double equals) and identity (=== triple equals) comparison operators differ?

Reference - What does this symbol mean in PHP?

php not equal to != and !==

What are the !== and === operators in this code snippet?

if ( $a !== null ) // do something
if ( $b === $a ) // do something

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They are identity equivalence operators.

1 == 1
1 == "1"
1 === 1
1 !== "1"
true === true
true !== "true"
true == "true"

All of these equate to true. Also check this link provided by @mbeckish

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They are strict type comparison operators. They not only check the value but also the type.

Consider a situation when you compare numbers or strings:

if (4 === 4) // same value and type
{
  // true
}

but

if (4 == "4") // same value and different type but == used
{
  // true
}

and

if (4 === "4") // same value but different type
{
  // false
}

This applies to objects as well as arrays.

So in above cases, you have to make sensible choice whether to use == or ===

It is good idea to use === when you are sure about the type as well

More Info:

• http://php.net/manual/en/types.comparisons.php

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=== also checks for the type of the variable.

For instance, "1" == 1 returns true but "1" === 1 returns false. It's particularly useful for fonctions that may return 0 or False (strpos for instance).

This wouldn't work correctly because strpos returns 0 and 0 == false

if (strpos('hello', 'hello world!'))

This, however, would work :

if (strpos('hello', 'hello world!') !== false)

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A double = sign is a comparison and tests whether the variable / expression / constant to the left has the same value as the variable / expression / constant to the right.

A triple = sign is a comparison to see whether two variables / expresions / constants are equal AND have the same type - i.e. both are strings or both are integers.

The same concept applies for !==

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They will only return true if both the type and value of the values given are equivalent. Example: 1 === 1 is true "1" === 1 is false 1 === "1" is false "1" === "1" is true

where as with == all of the above would be true

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When you use two equal signs == it will check for the same value.

if( '1' == 1 ) { echo 'yes'; }

The above code works because they have the same value.

But if you use three equal signs === it will check the value and the data type.

Therefore

if( '1' === 1 ) { /* this will not work */ }

This is because '1' has a data type of string while 1 is an integer or a number

But you could do something like this - I think :D

if( (integer) '1' === 1 ) { echo 'this works'; }

Because we are changing the data type of '1' to an integer